If you have made sure your drivers are up to date, and have a clean install, a couple of things come to mind.
Outdated version of Direct X
Out of memory
Inadaquate video card (and video card memory)
Possible heat issues
Dont want to hear it runs this or that just fine, SH4 is one of the most 'stressful' games around.
Do us a favor and visit this site
http://www.systemrequirementslab.com/referrer/srtest
Select SH4 and run the test and get back to us.